WASHINGTON (Reuters) - Prescriptions for hormone replacement therapy have fallen more than 50 percent in the United States since 2001, but doctors are still inexplicably giving women high-dose pills linked to strokes and cancer, researchers reported on Thursday.

The U.S. Food and Drug Administration and other groups do not say women should avoid hormone replacement therapy, or HRT, but they recommend taking the lowest possible dose for the shortest period of time.

"We're disappointed," Dr. Randall Stafford of Stanford University in California, who led the study, said in a statement.

"Yes, there was an increase in the use of low-dose preparations, but it was not sizable."

Hormone replacement therapy is used by women who are going through or who have gone through menopause to relieve symptoms that range from hot flashes, low energy, sleeplessness and vaginal dryness to bone loss.

Doctors once believed HRT also prevented heart disease and cancer, but the Women's Health Initiative found in 2002 that women who took estrogen plus progesterone pills for five years had higher rates of ovarian cancer, breast cancer, strokes and other health problems.

Sales of U.S. market leader Wyeth's combined estrogen plus progesterone pill Prempro have fallen by about 50 percent since 2001 to around $1 billion a year. Wyeth is now owned by Pfizer.

Many makers of HRT have reformulated their products, offering much lower doses of hormone, often as patches, creams or vaginal delivery products.

Stafford and colleagues looked at data from 340,820 patient visits to hospitals, clinics and doctor's offices, as well as information from telephone calls.

They found that use of HRT fell by 52 percent from 2001 to 2009, from 17.5 million users to 8.3 million users. But the women using HRT were often still getting relatively high doses of hormones in the pills.

"Despite reduced use, standard-dose oral (HRT) remains the dominant formulation, yet lower-dose transdermal and vaginal preparations may yield less harm," they wrote in Menopause: The Journal of the North American Menopause Society.

"We thought that over time there might be greater tailoring of therapy based on characteristics of the individual woman," Stafford said. "The bottom line is that over time we didn't see the level of refinement in clinical practice that we expected."

Many experts believe that lower-dose formulations and skin patches may be a safer way to deliver HRT. The patches, in particular, may reduce the amount of hormones reaching vulnerable organs.

In 2001, more than 16 million women took some form of HRT pill, but by 2009, 6 million did, the survey found.

Lower-dose product use increased modestly, from 700,000 in 2001 to 1.3 million in 2009, they found.

In October, researchers reported that women who took hormone replacement pills had more advanced breast cancers and were more likely to die from them than women who took a dummy pill. In June, a different team found that women using low-dose patches were less likely to have strokes than women taking pills.